A hormone, and a neurotransmitter, that regulates heart rate, blood vessel and air passage diameters, and metabolic shifts and that is a crucial component of the fight-or-flight response of the sympathetic nervous system.
The sense of the positions of body parts relative to other neighboring body parts.
Researchers have developed several theories of how human emotions arise and are represented in the brain. The James–Lange theory of emotion, for instance, asserts that emotions arise from physiological arousal: in essence, that the self-perception of changes in the body produce emotional experiences. According to this theory, we laugh (a physiological response to a stimulus), and consequently we feel happy (an emotion); we cry, and consequently we feel sad.
For example, if you were to encounter a venomous snake in your backyard, your sympathetic nervous system (responsible for activating your fight-or-flight response) would initiate physiological arousal, making your heart race and increasing your breathing rate. According to the James–Lange theory of emotion, you would experience a feeling of fear only after this physiological arousal had taken place. Different arousal patterns would be associated with different feelings.
One limitation of this theory is that it is not known exactly what causes the changes in the body, so it is unclear whether those changes should be considered part of the emotion itself. Critics of the James–Lange theory also doubt that there is sufficient variation in physiological arousal to lead to the wide variety of emotions that we experience. To address these limitations, other theories—such as the Cannon–Bard theory—have been developed.